Heretofore, a halogen-based flame retardant containing halogen groups, such as chlorine and bromine, has been the mainstream in terms of a flame retardant for flammable materials, for example, various resin materials which are organic polymer materials, or fibers such as lumber, paper, cloth, textiles and nonwoven fabrics. The halogen-based flame retardant is widely used for various building materials, household electrical appliances, automobiles, aircrafts, trains, electric wire materials and the like since it is excellent in balance between flame retardancy and material cost.
However, flame retarding technologies using no halogen-based flame retardant have intensively been developed recently because of such problems as the influence of a combustion gas containing halogen and generation of dioxins due to incineration upon disposal. Among these, a flame retardant using phosphoric acid or boric acid, a method of insulating by forming a foamed film, a flame retardant containing a high concentration of a metal hydrate such as magnesium hydroxide and aluminum hydroxide, or a nonhalogen-based flame retardant as a composite thereof have appeared in a market.
As a nonhalogen-based flame retardant, a nonhalogen-based flame retardant composed mainly of a metal hydrate such as magnesium hydroxide and aluminum hydroxide is mainly used. The metal hydrate is commercially produced in place of the halogen-based flame retardant. For example, a nonhalogen-based flame retardant composed mainly of magnesium hydroxide has satisfactory flame retardancy. Therefore, it is preferably used for electric wire coating of automobile wire harnesses, internal wiring of appliances and power source cords, which require high flame retardancy and mechanical strength.
However, where a nonhalogen-based flame retardant composed mainly of metal hydrate is used in a flame retardant composition, the composition must contain the metal hydrate in large amount so as to exhibits flame retardancy equivalent to that of the flame retardant composition containing a halogen-based flame retardant. However, when the flame retardant composition contains a large amount of the metal hydrate, abrasion resistance, low temperature characteristics and mechanical strength, such as tensile breaking strength or tensile breaking elongation, of a molded article deteriorate. Furthermore, the flame retardant composition containing a high concentration of the metal hydrate is likely to cause peeling at the interface between the metal hydrate and a resin and the obtained molded article is drastically whitened, and also flexibility of the molded article deteriorates.
Therefore, in the nonhalogen-based flame retardant composed mainly of the metal hydrate, it is required to develop those, which enables a good balance between mechanical strength and flexibility of the molded article of the flame retardant resin composition by reducing the content of the metal hydrate, and still can secure sufficient flame retardancy.
To meet such a requirement, Patent Document 1 proposes a flame retardant composition comprising an α-olefin (co)polymer, an ethylene (co)polymer or a rubber, a metal halide such as magnesium hydroxide or aluminum hydroxide, and a polymer having a carboxylic acid group.
Patent Document 2 proposes a flame retardant composition of an olefin-based resin, which has high flame retardancy imparted by adding a small amount of a silicone resin to a metal hydrate such as magnesium hydroxide.
Patent Document 3 proposes a flame retardant composition comprising a polyolefin-based resin with the addition of a metal hydrate, such as magnesium hydroxide or aluminum hydroxide, and a small amount of an organic clay.
In the flame retardants described in Patent Document 2 and Patent Document 3, magnesium hydroxide having a small particle diameter of about 1 μm is preferably used as the metal hydrate.    Patent Document 1: Japanese Unexamined Patent Application, First Publication No. Hei 5-239281    Patent Document 2: Japanese Unexamined Patent Application, First Publication No. Hei 5-54723    Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2003-197043